AERONET and ESR sun direct products comparison performed on Cimel CE318 and Prede POM01 solar radiometers

Abstract

Abstract. The European Skynet Radiometers network (EuroSkyRad or ESR) has been recently established as a research network of European Prede POM sun – sky radiometers. Moreover, ESR is federated with SKYNET (SKYrad NETwork), an international network mostly present in East Asia. In contrast to SKYNET, the European network also integrates users of the Cimel CE318 sunphotometer. Keeping instrumental duality in mind, a set of open source algorithms has been developed consisting of two modules for: (1) the retrieval of direct sun products from the sun extinction measurements; and (2) the inversion of the sky radiance to derive aerosol optical properties. In this study we evaluate the ESR direct sun products (spectral aerosol optical depth, Angström wavelength exponent and columnar content of water vapour) in comparison with the AERosol RObotic NETwork (AERONET) products. Specifically, we have applied the ESR algorithm to a Cimel CE318 and Prede POM01L simultaneously for a 4 yr database measured at the Burjassot site (Valencia, Spain), and compared the resultant products with the AERONET direct sun retrievals obtained with the same Cimel CE318 instrument. The comparison show that aerosol optical depth differences are mostly within the nominal uncertainty of 0.003 for a standard calibration instrument, and fall within the nominal AERONET uncertainty of 0.01–0.02 for a field instrument. Therefore, we present an open source code that can be used for both radiometers and whose results are comparable to those of AERONET and SKYNET.